Frans Steyn will replace Zane Kirchner in the South Africa team to play Wales in Cardiff on Saturday. Photograph: Duif du Toit/Gallo Images/Getty Images

Some of South Africa's performances in this year's Tri-Nations were X-rated horror shows, as they fell from top to bottom, but on Saturday against Wales in Cardiff they will be relying on the X-factor to keep them on course for a grand slam over the home unions.

The Springboks have made one change from the side that defeated Ireland in Dublin for their second appearance at the Millennium Stadium in five months with Frans Steyn, who was on club duty with Racing Métro last weekend, replacing Zane Kirchner at outside-centre.

"We were not tested a lot in Dublin and Zane did not let us down but Frans has the X-factor that you need in Test matches," said the South Africa coach, Peter de Villiers, who has not always enjoyed the warmest relationship with the outspoken Steyn. "There are two things you cannot buy in rugby – speed and the outstanding talent Frans has. If a player like him is available, it is a waste if you put him on the bench.

"We were not challenged a lot on Saturday and I expect Wales to make changes from the side that played Australia, looking to speed up their game. I think they will opt for a quicker player than Mike Phillips at scrum-half and they have to decide whether to play James Hook, who can bring wide players into the game, at 10."

De Villiers said he did not care whether Wales kept the Millennium Stadium roof open or closed. "It does not bother me. The closer you stay to the natural conditions the better it is for the game and it will teach us how to adapt to the conditions in New Zealand next year. If we look at this tour in isolation we are lost – we have to make use of everything that nature and teams throw our way before the World Cup."

Wales will name their team tomorrow. They will have to make at least once change from Australia with the flanker Sam Warburton ruled out for up to three weeks with a torn calf muscle while the full-back Lee Byrne and the No8 Ryan Jones have returned to training and are expected to be fit for Saturday.

"It is a big boost to see Lee and Ryan in training," the Wales forwards coach, Robin McBryde, said. "We are not blessed with a great amount of depth and they would be a big plus for us. Sam's injury is unfortunate because he was outstanding against Australia.

"We set down a marker against the Wallabies and we are looking to build on that. South Africa are perhaps the Tri-Nations team that has reacted slowest to the new interpretations of the law and the way the game has gone. I am sure they are working hard to make up the ground they have lost, in the eyes of some, to Australia and New Zealand.

"They looked comfortable against Ireland and they will be tough at the set piece. We adapted against Australia and made subtle changes to our gameplan. South Africa offer a more physical, direct threat and we have to tailor our approach in defence and attack to match them. Our front row played for the Lions against South Africa last year and our scrum has become something we can call a weapon."